Multilayer heat sinks are now commonly incorporated into high performance microelectronic packages prone to excess heat generation during operation. Generally, a multilayer heat sink is produced by bonding multiple metallic layers in a stacked or laminated configuration. The composition and number of metal layers are chosen to impart the multilayer heat sink with a relatively high thermal conductivity suited for heat dissipation purposes, while further imparting the heat sink with an effective Coefficient of Thermal Expansion (CTE) more closely matched to the microelectronic device or devices (e.g., semiconductor die) supported by the heat sink. To provide a more specific example, a multilayer heat sink might include an upper copper (Cu) layer, a lower Cu layer, and an intervening layer disposed between the upper and lower Cu layers. The intervening layer is composed of a metallic material having a CTE less than that of the Cu layers, such as molybdenum (Mo) or a copper-molybdenum (Cu—Mo) alloy. By virtue of the inclusion of the intervening Mo or Cu—Mo layer, the effective CTE of the multilayer heat sink may be lowered to reduce mechanical stresses occurring within the microelectronic package (particularly, at the heat sink-die attach interface) through thermal cycling. Concurrently, the overall thermal conductivity and, thus, the heat dissipation characteristics of the multilayer heat sink may remain comparable to that of a monolithic heat sink wholly composed of Cu, a Cu-based alloy, or a similar material.
For simplicity and clarity of illustration, descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the exemplary and non-limiting embodiments of the invention described in the subsequent Detailed Description. It should further be understood that features or elements appearing in the accompanying figures are not necessarily drawn to scale unless otherwise stated. For example, the dimensions of certain elements or regions in the figures may be exaggerated relative to other elements or regions to improve understanding of embodiments of the invention.